According to the technology of the prior art for the production of monomer vinyl chloride by the cracking of dichloroethane, this latter is pre-heated, vapourized, overheated and cracked inside one single piece of equipment heated by combustion (oven) and heat exchange by irradiation and convection from the combustion products towards the stream of dichloroethane. According to this technology, the enthalpy contained in the reaction products at the outlet of the oven, at the typical temperatures of from 450.degree. to 550.degree. C., is no longer used in the plant; the stream of outflowing products is quickly cooled to decrease the reaction rate of undesired reactions, but the enthalpy is not recovered for purposes useful to the system. Furthermore, according to the technology of the prior art, the stream of dichloroethane is vapourized inside the same oven, while being in contact with the combustion products at very high temperature, causing the production of dichloroethane breakdown products, among which coke and coal, which act as precursors of formation of further coke and coal in the irradiation section, which in its turn is quickly fouled up to render the oven no longer operable if not to prejudice of its integrity; the equipment must be hence shut off and submitted to the decoking operation to clean the inner surface of the tubes, with a frequency of about 3-5 times a year.
A variant of the known technology consists in vapourizing the charge in a heat exchanger external to the oven, by using steam, the consumption of which becomes however a considerable expenditure item among the plant consumptions, by it being always produced at expense of valuable fuels.
It has been surprisingly found that reducing the consumptions of fuel is possible, by using the enthalpy of the efficent from the oven to the purpose of both vapourizing the charge and overheating the combustion air, and that increasing is possible the operating time between two subsequent over decoking operations, by very quickly cooling the efficent from the oven and vapourizing the charge by a high-temperature source at a temperature lower than of the fumes of the known art.
A first object of the present invention is a process for the production of monomer vinyl chloride by dichloroethane cracking, comprising feeding a stream of dichloroethane to the convective section of an oven, so to heat it up to a temperature lower than its boiling temperature under the pressure used, vapourizing the dichloroethane stream outflowing from the convective section of the oven in an area external to said oven, by indirect heat exchange with a hot gaseous fluid, selected from the oven combustion products nitrogen and/or air, either alone or as mixtures with one another, heated by indirect heat exchange with the hot dichloroethane breakdown (cracking) products outflowing from said oven, drawing the stream of vapourized dichloroethane from said external area, and introducing it into the radiant section of said oven, the heat in the radiant section being supplied by the combustion of an either liquid or gaseous fuel with a comburent in particular constituted by a portion of the air heated by indirect heat exchange with the hot dichloroethane cracking products outflowing from said oven, if said air has been used as the high-temperature gaseous fluid for indirect heat exchange.
A second object of the present invention is an equipment system suitable to carry out the above disclosed process.